It is generally known that dihydroxyacetone, when applied topically to human skin, will produce a tanned appearance, i.e. an artificial tan. U.S. Pat. No. 4,708,865, to Turner, issued Nov. 24 , 1987 describes the use of hydro-alcoholic solutions of dihydroxyacetone for tanning the skin; U.S. Pat. No. 4,466,805, to Welters, issued Aug. 21, 1984 describes hair and skin coloring formulations containing dihydroxyacetone; and U.S. Pat. No. 2,949,403, to Andreadis et al., issued Aug. 16, 1960 describes artificial tanning formulations containing dihydroxyacetone in an oleaginous base. However, it is also known that emulsion products containing dihydroxyacetone have a short shelf life, tending to darken and develop disagreeable off-odors over time with a concomitant loss of emulsion integrity. Dihydroxyacetone is relatively sensitive to heat, light, moisture, and alkaline pH. Dihydroxyacetone can react with other ingredients in a formulation, especially with nitrogen-containing compounds, such as amines, amino acids, and the like. In fact, without being limited by theory, dihydroxyacetone is believed to provide an artificial tan to human skin by its reaction with the nitrogen containing proteins of the skin. See L. Goldman et al., "Investigative Studies with the Skin Coloring Agents Dihydroxyacetone and Glyoxal", The Journal of Investigative Dermatology, vol. 35, pp 161-164 (1960); and E. Wittgenstein et al., "Reaction of dihydroxyacetone (DHA) with Human Skin Callus and Amino Compounds", The Journal of Investigative Dermatology, vol. 36, pp. 283-286 (1961).
The manufacture of liposomes, i.e. lipid vesicles, and their use for the delivery of a wide variety of materials is well-known. See Gregoriadis, G., ed. Liposome Technology vols. 1-3, 1984 (CRC Press, Boca Raton, Fla.). Most of the commonly used liposomes are single-layered vesicles prepared from phospholipids. The reason for this is that phospholipids are the principal structural components of natural membranes. However, phospholipids are susceptible to enzymatic degradation, autoxidation, and acidic pH conditions, and are exceedingly expensive to prepare. Furthermore, phospholipid vesicles are relatively fragile, tending to rupture, coalesce, and release their encapsulates. To avoid these disadvantages, there has been a movement towards the development of multilayered (i.e. multilamellar) vesicles prepared from a variety of lipids and surfactants. However, multilayered vesicles are generally more difficult to produce than conventional liposomes, and their encapsulation volumes tend to be small. Paucilamellar lipid vesicles overcome the disadvantages of conventional multilayered liposomes by providing both a stable multilayered lipid structure and a relatively large central cavity. Paucilamellar lipid vesicles are described in U.S. Pat. No. 4,911,928, to Wallach, issued Mar. 27, 1990. Furthermore, paucilamellar vesicles are especially suited for encapsulating aqueous solutions of hydrophilic materials. In particular, paucilamellar vesicles made by replacing conventional phospholipids with acid-stable/compatible surfactants such as polyoxyalkylene alkyl ethers have the additional advantage of providing an acid-stable liposomal system useful for encapsulating acidic materials such as dihydroxyacetone in formulations having an acidic pH.
Currently available artificial tanning products have the disadvantage of not providing the desired control over color development of the tan. Artificial tans are often either too light or too dark, and tend to be too orange, uneven, or unnatural in appearance. Furthermore, artificial tans tend to take too long to develop, and once obtained, tend to fade too quickly and unevenly. Therefore, it would be highly desirable to provide dihydroxyacetone containing products which are chemically and physically stable, which are aesthetically pleasing, and which overcome these color development limitations. Products which overcome these disadvantages can be achieved through the use of paucilamellar liposome systems for delivering dihydroxyacetone from an oil-in-water emulsion composition.
Sunscreens are the most common agents used for sun protection. However, sunscreens also have the disadvantage of preventing or greatly diminishing the cosmetically desirable tanning response. Therefore, it would be highly desirable to provide protection from the harmful effects of ultraviolet radiation, and yet at the same time deliver a tanned appearance to the skin.
Furthermore, even if an individual is willing to accept the risks associated with exposure to ultraviolet radiation in order to obtain a tan, there are situations in which it may not be practical or even possible to do so because of time constrains, weather conditions, time of day, season of the year, geographic limitations, unavailability of an artificial ultraviolet radiation source, and the like. Therefore, it would be highly desirable to provide products that can deliver a tanned appearance whenever desired, without the need for ultraviolet radiation.
It is therefore an object of the present invention to provide oil-in-water emulsion compositions containing dihydroxyacetone in paucilamellar vesicles for imparting an artificial tan to human skin. Another object of the present invention is to provide emulsion compositions for imparting an artificial tan which exhibit a high degree of chemical and physical stability and which are aesthetically appealing to consumers. A further object of the present invention is to provide compositions for both imparting an artificial tan to human skin and also for protecting the skin from ultraviolet radiation. A still further object of the present invention is to provide a method for artificially tanning human skin. It is another object of the present invention to provide a method for both artificially tanning human skin and for providing protection against ultraviolet radiation.
These and other objects of this invention will become apparent in light of the following disclosure.